(VAR X Y Z )
(RULES 
        primes -> sieve(from(s(s(0))))
        from(X) -> cons(X, from(s(X)))
        head(cons(X, Y)) -> X
        tail(cons(X, Y)) -> Y
        if(true, X, Y) -> X
        if(false, X, Y) -> Y
        filter(s(s(X)), cons(Y, Z)) -> if(divides(s(s(X)), Y), filter(s(s(X)), Z), cons(Y, filter(X, sieve(Y))))
        sieve(cons(X, Y)) -> cons(X, filter(X, sieve(Y)))
        
)